O.bodies.append(utils.sphere([0,0,0],1,dynamic=True))
O.engines=[
    ForceResetter(),
    PyRunner(command='O.forces.addMove(0,(1e-2,0,0))',iterPeriod=1),
    NewtonIntegrator()
]

for i in range(0,20):
    O.step()
    print(O.forces.f(0),O.bodies[0].state.pos)
quit()
